Method for vacuum casting of steel



Jan. 15, 1963 o. w. AHMANSSON ETAL METHOD FOR VACUUM CASTING OF STEELOriginal Filed July 31, 1958 United States Patent ()fince 3,072,985Patented Jan. 15, 1953 3,072,985 METHOD FOR VACUUM CASTING OF STEEL OlovWood Ahmansson, Goteborg, and Lars Olof Uhrus, Hotors, Sweden, assignorsto Aktiebolaget Svenska Kuliagerfabriken, Goteborg, Sweden, acorporation of Sweden Continuation of application Ser. No. 752,293, July31, 1958. This application Feb. 3, 1960, Ser. No. 6,568 4 Claims. (Cl.22-215) This invention rel-ates broadly to casting of metals and morespecifically to casting of metals in vacuum.

In casting steel or other metal in vacuum, the procedure is generally asfollows: The molten metal passes from a receptable, a so-called ladle,in a jet or stream down into a chiller which is located in a receivingreceptacle. With the aid of suitable pumps the right amount of vacuum iscreated in the receptacle, for which purpose a vacuum-tight cover isarranged between the ladle and the receptacle. If proper vacuum is to beobtained, it is important, among other things, that the receptaclecontains no porous material in which gas can be occluded in surface andpores.

Previously in vacuum casting steel, for example, there was no advantagein using the hot tops generally used when casting in a chiller, whichare made of fire-proof material with the lowest possible capacity forheat-conduction, since these materials are always porous and have anunfavorable effect on the vacuum treatment, in that it takes a very longtime to remove the quantities of gas present in the pores of thematerial. The quantity of gas emitted from the fire-proof material isincreased by the moisture always remaining in the material. Theunfavorable eftect of the fire-proof material is accentuated if thematerial is heated, for instance, when molten metal comes in contactwith the material.

The present invention relates to a process for vacuum casting steel in achiller, and has as a primary object elimination of the difiicultiesassociated with the use of fire-proof material for insulating the toppart of the ingot in connection with the vacuum treatment of moltenmetal. The object of the invention is chiefly attained by the fact thatduring the casting process the chiller is provided with a removableupper part of non-porous material, preferably of the same material asthe chiller, such as cast iron and which, after the molten metal issuitably cooled, is replaced by a suitable layer or protective hood orthe like covering the top part of the ingot or casing, the layer beingof porous thermoprotective material.

Additional objects and advantages of the invention will be more fullyappreciated from the following detailed description of embodimentsthereof, when taken together with the accompanying drawings, in which:

F6. 1 is a schematic view of one form of apparatus for vacuum casting ofmetal;

FIG. 2 is a fragmentary sectional view of a chiller mold with non-poroustop part;

FIG. 3 is a fragmentary sectional view corresponding to FIG. 2 with anon-porous top part replaced by a thermo-pro-tective top;

FIG. 4 is a fragmentary sectional view or a modification having the toppart enclosed in an outer steel casing;

FIG. 5 is a fragmentary sectional view corresponding to FIG. 4 with thetop part replaced by a thermo-protective covering;

FIG. 6 is a fragmentary view partly in section of a further modificationincorporating means for introducing exothermal reactant material to theingot;

FIG. 7 is a fragmentary view partly in section of a further modificationincluding heating means for the casting top;

FIG. 8 is a fragmentary view partly in section of a furdthermodification incorporating different heating means; an

FIG. 9 is a view taken on line 9-9 of FIG. 8.

Referring to the drawings, a usual type of chiller mold 10 is mounted ona base 12 within a lower portion of a receiving receptable 14. Means areprovided for closing and sealing the upper end of the receivingreceptable and as shown may include a casing 16 formed as a portion of aladle 18 of any known type having a molten metal discharge spout 20.Co-acting flanges 22 and 24 on the member-s 16 and 14 respectively serveto establish a vacuum tight interior for the receiving receptable. Avacuum pump 26 operatively associated with a motor 28 acting throughpipe 30 and valve 32 function to create the desired amount of vacuum inthe receiving receptacle.

In accordance with the present invention the chiller mold 19 isprovided, before casting of the metal, with a toward its upper end.Hooks 36 or the like are provided for facilitating movement of the top.During the casting process the chiller mold after being placed in thereceiving receptacle is provided with the top part 34 in place. A vacuumis then drawn in the receptacle and molten metal discharged into thechiller mold. When the vacuum treatment of the molten metal has beencompleted, when the chiller is filled, the receiving receptacle isconnected with ambient air through the valve 32 which serves at the sametime to cut off the vacuum pump from connection with the receptacle.

As soon as possible, that is when a thin layer of hardened material hasformed against the top part 34, this top part is removed from thechiller mold. Immediately following this, a covering for the upper partof the casting is provided. In the embodiment shown in FIG. 3 thisincludes a cylindrical shaped casing 38 which rests on the top surfiaceof the chiller mold and has a cross section such that a considerable gapremains between the casting shown at 40 and the inner surface of thiscasing 3 8. The space is quickly filled with a suitablethermo-protec'tive material 42, for example kieselguhr powder, whichmaterial should also cover the top surface of the ingot or casting inorder to retain the heat as long as possible.

The modification shown in FIGS. 4 and 5 differs from that shown in FIGS.2 and 3 in that a casing 44 is fitted around the top part of the chillermold 10 prior to the casting process and can if desired be secured tothe mold. At a suitable time during cooling of the metal, it is thusonly necessary to lift 01f the top part 34 and fill the ring shapedspace thus formed between the casing 44 and the ingot or casting 40 withsuitable thermo-protective material 42 which, as in the previousembodiment, preferably should cover the top surface of the casting oringot.

The top part or cover 34 can if desired be connected with the ladledirectly so that the chiller and cover together form the receivingreceptacle. It would thus not be necessary to use a special oradditional receiving re ceptacle and the volume which must be evacuatedwill be reduced to a minimum. For this purpose the top part would beprovided with an evacuation opening and the necessary seals.

The sheet iron cover and the loos-e film of kieselguhr powder can bereplaced by other suitable insulating films or covers, such as afinished and suitably-tapered hood, closed at the top, and which isplaced over and around the top of the casting or ingot after thenon-porous top part has been removed.

In FIG. 6 such a hood is shown at 46 and is suitably receptacle duringthe vacuum treatment.

designed so that an intenspace is formed between it and the top part ofthe ingot. It is advisable to have a supply of heat in this space. As anexample, holes in the top of the hood permit introduction of anexothermal mixture from a header 52 connected through a conduit 54 to asuitable source. After the hood has beenplaced over the ingot, areaction is thusstarted when the mixture contacts the ingot which isstill glowing at the top.

Another method of supplying heat to the top of the ingot is shown inFIG. 7, where a hood 56 is provided internally with a resistance heatingelement 58 of any desired known type such as embedded in porcelain 6t),the inner surface of which is spaced from the ingot as shown at 62. Thisarrangement additionally permits preheating the hood 56 before itisplaced over the ingot.

In FIGS. 8 and 9, a further type of hood 64 is shown having-inlet burnerjets 66 arranged tangentially with respect to the hood for theintroduction into space 68 of gas or oil. These jets are arranged nearthe lower edge. of hood 64 and exhaust gases can be drawn ofi throughopening 70 in the top 72 of the hood.

In accordance with the present invention it is possible to obtainsatisfactory insulating of the top part of the ingot or casting duringthe principal part of the period required for the: complete hardening orthe ingot and prevent any porous material from being in the receivingAdditionally, no molten metal can get in contact with the fire-proofmaterial in the vacuum chamber itself.

Manifestly minor changes can be effected in the method and describedapparatus without departing from the scope and spirit 'ofthe' inventionas defined in the appended claims.

This application is a continuation of our application Serial No.752,293, filed July 31, 1958, now abandoned.

We claim:

1. A method of casting metal which comprises introducing molten metal toan upright mold of non-porous material having a removable, open-endedupper portion located within an evacuated chamber, removing said upperportion of said mold to expose the upper end of said cast metal as soonas a thin layer of solidified metal has formed against the upper portionof said mold, and immediately surrounding the exposed upper end of saidcast metal with porous heat-insulating material, while maintaining saidcast metal in the lower portion of said mold in the position initiallyassumed with respect thereto. as when initially cast in said mold, andcompleting solidifying said cast metal, said porous heat-insulatingmaterial being applied to the exposed end of said cast metal afteradmission of air to said chamber.

2. The method according to claim 1, wherein said porous heat-insulatingmaterial is maintained in surrounding relationship with the exposedmetal by means of a jacket.

3. A method according to claim 2, wherein the jacket is'applied to themold only after the upper non-porous part of the mold has been removed.

' 4. The method according to claim 2 wherein said jacket comprises anintegral part of the lower portion of said mold.

References Cited in the file ofthis patent UNITED STATES PATENTS1,431,804 Howard et a1 Oct. 10, 1922 1,978,996 Gathmann Oct. 30, 19342,102,258 D ornin Dec. 14, 1947 2,885,751 Hornak et a1. May 12, 1959FOREIGN PATENTS 866,231 Germany Feb. 9, 1953 1,173,413 France Oct. 27,1958 OTHER REFERENCES Gathmann: The Ingot Phase of Steel. Production,pp. 30, 31, 1942.

1. A METHOD OF CASTING METAL WHICH COMPRISES INTRODUCING MOLTEN METAL TOAN UPRIGHT MOLD OF NON-POROUS MATERIAL HAVING A REMOVABLE, OPEN-ENDEDUPPER PORTION LOCATED WITHIN AN EVACUATED CHAMBER, REMOVING SAID UPPERPORTION OF SAID MOLD TO EXPOSE THE UPPER END OF SAID CAST METAL AS SOONAS A THIN LAYER OF SOLIDIFIED METAL HAS FORMED AGAINST THE UPPER PORTIONOF SAID MOLD, AND IMMEDIATELY SURROUNDING THE EXPOSED UPPER END OF SAIDCAST METAL WITH POROUS HEAT-INSULATING MATERIAL, WHILE MAINTAINING SAIDCAST METAL IN THE LOWER PORTION OF SAID MOLD IN THE POSITION INITIALLYASSUMED WITH RESPECT THERETO AS WHEN INITIALLY CAST IN SAID MOLD, ANDCOMPLETING SOLIDIFYING SAID CAST METAL, SAID POROUS HEAT-INSULATINGMATERIAL BEING APPLIED TO THE EXPOSED END OF SAID CAST METAL AFTERADMISSION OF AIR TO SAID CHAMBER.